Water purifying filter aid



'April 26, 1949.

C. A. FRANKENHOFF WATER PURIFYING FILTER AID Original Filed June '7,1945 3 Sheets-Sheet 1 Hr 28 29 I CIA. FRANKENHOFF INVENTOR.

BY via Q.

A TORNE) April 26, 1949. c. A. FRANKENHOFF WATER PURIFYING FILTER AID '6Sheets-Sheet 2 Original Filed June 7, 1945 INVENTOR.

i TORNEY April 2 1949- c. A. FRANKENHOFF 2,468,189

WATER PURIFYING FILTER AID Original Filed June '7, 1945 '3 Sheets-Sheet3 FRANK E NH OFF IN VENT OR.

BY M

Patented Apr. 26 1949 WATER PURIFYING FILTER AID Charles A. Frankenhofl,Scarsdale, N. Y., assignor to Great Lakes Carbon Corporation, acorporation of Delaware Original application June 7, 1945, Serial No.598,006. Divided and this application February 5, 1946, Serial No.645,659

2 Claims. 1 The instant application is a. division of my copendingapplication Serial No. 598,006, filed June '7, 1945, and entitledClarification of water supplies.

This invention relates primarily to the clarifi the quantity of liquidto be clarified is moderate cation of water in large quantities fordomestic 1- and industrial purposes and to methods and materialstherefor.

The invention relates also to the intensive purification of highlycontaminated waters to render them potable, as for the use of troops inthe field.

The invention relates also to the clarification of boiler feed waterscontaining minute quantities of finely dispersed lubricating oils,specifically to render such waters fit for reuse on shipboard.

and the cost of filtration is justiiied by the Value of the liquid, buthas been recognized as wholly impracticable for the purification ofdomestic and industrial waters. Those filter-aids which are sufficientlyfree flowing to be employed for this purpose do not remove the finersediments such as colloidal clays, dispersed oil or colloidal organicmatter, while such as yield a clear filtrate have a flow rate so limitedas to require a filtration plant too costly to be practicable for indus-In general terms, the invention lies in simultaneously introducing intoa stream of the water to be clarified minute amounts of a diatomaceousearth filter-aid and of a salt forming a fiocculent precipitate in thepresence of basic substances, in thus producing a precipitate in whichthe earth particles are coated with insoluble gelatinous matter, and inpassing the stream through a filter on which the precipitate is built upinto a free filtering cake having an abnormally high clarifying power,the water stream emerging from the filter in a high degree of purity.

It is old practice to add salts of iron or aluminum to water for thepurpose of producing a flocculent precipitate therein, and thereafter tofilter out the fioc in sand beds, usually after settling the majorportion of the fioc in sedimenting basins. This method is efiectivewhere space and weight are not a consideration, producing a degree ofclarification which is suflicient for most industrial and domesticpurposes. It is useless, however, for any service in which portabilityis required because of the space required and the great weight of thesand beds, which have a very low unit capacity where gravity flow isused. Any attempt to apply pressure to the water to increase thethroughput of the. sand bed results in the carrying of floc through thefilter, thus destroying the clarity of the filtrate. Nor can these flocsbe filtered out on twill or other filtering cloths as they glaze overand seal the cloth almost immediately after the establishment of a clearfiltrate.

It is also well known to filter many aqueous liquids with the use of adiatomaceous earth filtier-aid. This practice is highly eficacious wheretrial or community water's.

I have discovered that by combining the use of fioccul'ating salts withthe use of diatomaceo'us earth filter-aids, in a certain specific mannerabout to be described, I' can so increase the relation between flow rateand clarifying power of the filter-aids as to render their use for thispur-- pose economically feasible and highly attractive.

The salts used for thispu-rpose may be any of the water-soluble salts ofiron, aluminum or chromium, all of these salts yielding flocculentprecipitates when added to water containing traces of basic substances.For practical purposes it is desirable to choose between the sulfates ofaluminum and of ferrous iron, these salts yielding the most voluminousprecipitates at the least cost.

The di atomaceous earth tiltenaid selected for this purpose should be agrade having a relatively high flow-rate. The e'ffiect oi the aluminumsalt, as will be described, is greatly. to enhance the clarifying powerwith only a moderate reduction in flow-rate. Thus a high throughput persquare root of filtering surface, without sacrifice of clarity, isobtained in the use of an earth having in itiall y a high flow rate, Thegrade of earth known commercially as Dicalite Speede is well adapted tothis use, or an even more free-flowing grade may be used.

The relationship between the quantities of salt and of earth to be addedto -the water are subject to some variation, being influenced to someextent by the characteristics of. the particular grade of earthemployed. A very free-fiowing earth having relatively low inherentclarifying power will require a greater proportion of the salt than an.earth having initially a lower flow rate. Ordinarily the weight of salt,figured as water-free aluminum sulfate, will be from 0.5% to 3.0% of thetotal Weight ofs'oiids' added.

' The relation between the total. quantity of ad.-

3 ditive and the weight of Water clarified will vary with the nature ofthe suspensoids to be removed and, to a lesser extent, with the quantityof suspended matter. The coarser suspensoids are removed withoutdifiiculty, whatever their quantity, by the mer straining action of thefilter cake, while the colloids must be entrapped and adsorbed by thegelatinous coatings on the diatoms of which the cake is composed. It isimpossible therefore, toreci-te any dosage which will be sufiicient forthe clarification of an unknown water, but it has been shown that adosage of as much as 1 pound of total additive per 1,000

gallons may be required to bring a water rendered highly turbid by anadmixture of ben-' tonite to a condition of zero turbidity (absolutebrilliance), this 1 pound consisting of 0.02 pound of aluminium sulfateand 0.98 pound diatomaceous earth. On the other hand, waters renderedturbid by the more common clays and silts may be brought to a fullysatisfactory clarity for domestic or industrial use with as little as {6pound per thousand gallons of the above additive.

It should be understood that the desirable results attained with'thismethod will not be had if the aluminum salt is added to the water asufilcient time in advance of the earth to allow the floc to form fullyand to begin to settle. The method is not a mere filtration of fioc froman alum treated water by the use of a filter-aid. That method willproduce a clear water but entails a large increasein the consumptions ofbothv salt and earth and material reductions in the rate of filter fiowand, in length of filtration cycle. On the contrary, the method requiresthe substantially simultaneous addition to the water of the twocomponents of the additive in order that the gelatinous aluminum or ironhydroxide may be precipitated on the individual particles of which thefilter-aid is composed. It is this floccoated earth which is effectivefor clarification to an extent and at a rate not heretofore attained.

' In the ensuing descriptions reference will be made to the appendeddrawings showing various methods of introducing the active agents intothe water stream and of conducting the filtration step to the bestadvantage.

In these drawings Fig. 1 illustrates diagrammatically a system in whichthe earth and the salt are mixed in advance, in proportioned quantities,and fed into the water stream as a dry mixture;

curves the behavior of the agents of the invention when used to clarifyboiler feed water.

Referring first to Fig. 1, dry comminuted earth is drawn from a bin H]by a measuring device such as a scroll feeder ll into a mixing trough I2provided with paddles. A weighed quantity of the salt, in the form of adry powder, is drawn from a bin l3 to give a. mixture of the desiredproportions. The batch is then thoroughly blended and drawn into aleeway bin from which it is fed at a measured rate by another scroll l5arranged to be rotated at an accurately controlled rate, into a conduitl6 through which the water to be clarified is flowing. This conr theearth mixture is throughout the water, which then passes to a duit leadsto the suction of a pump IT in which intimately dispersed filter I 8 inwhich the suspensoids are removed from the water and collected as afilter cake. The clarified water is delivered through a conduit I9 andat necessary intervals the cake is washed down and discharged throughconduit 20 in the form of a slurry, as will later be de- Fig. 2 is aflow sheet of a system in which the mixed agent is brought to the formof an aqueous slurry before being introduced into the water stream;

Fig, 3 similarly illustrates a system in which the agents are separatelyfed into the water stream;

Fig. 4 illustrates in plan and Fig. 5 in elevation a morecompleteassemblage of apparatus for handling large volumes of water fordomestic or industrial purposes;

Fig. 6 is a vertical section through one of the filters 40of Figs. 4 and5;

Fig. 7 is a section through a fragment of the actual filtering elementof Fig. 6;

" Fig. 8 is a diagram of an installation particularly adapted to theclarification of boiler feed water, shown in elevation;

Fig. 9 is a face elevationof one of the filtering elements 16 of Fig.8,with portions of the filtering and supporting media removed, and

Fig. 10 illustrates'b-y means of time v. pressure scribed.

This method may be modified by introducing the salt to the earth in theform of a saturated solution, permitting the quantity added to themixing trough to be gauged instead of weighed. The quantity of water soadded to the earth may be neglected unless the proportion of salt isrelatively large, in which case a light drying effect may be produced bygently heating the mixer after blending.

The advantage in this step of mingling the constituents of the combinedagent is to permit the separation of the step of blending from those ofuse, the mixture being subject to storage and transportation. It ishighly convenient where the clarifyin operation is conducted on amoderate scale and is almost essential in confined spaces, as onshipboard, but is poorly adapted to large scale operations such as theclarification of community Water supplies.

A modification of the above method which is particularly adapted to theclarification of condensed water containing finely dispersed steamcylinder lubricants is illustrated in Fig. 2. The dry agents, eitherpremixed or in proportioned quantities, ar introduced as at 2| into aslurry tank 22 supplied with water as at 23 and provided with an airblast 24 or other means for agitating the contents. In this tank the dryagent is brought to the condition of a slurry, which is then pumped intothe filter to form a precoat of desired thickness, a valve 25 beingprovided to shut off the Water supply during precoating. The slurry isthen followed through by water containing suspended oil, which for aconsiderable time will emerge oil free and brilliant.

After a time which varies with the thickness of the cake and the rate offlow the cake will become saturated with suspended oil, which willthereafter emergefrom the cake in the form of floating droplets ofappreciable size, the water in which these droplets are suspended beingstill brilliant. The mixed stream of water and oil drops is deliveredthrough a conduit 26 into a gravity separator 21 which should beprovided with a gas vent 28, an oil overflow 29 and a water drain 30. Inthe absence of solid suspensoids the treated cake so established willdeliver free oil and perfectly clear water 0 a long time withoutrecharging.

A modification adapted to the clarification of water in large quantitiesis illustrated in the flow two; agents intothe. condition of a thinslurry, a s-describedin connection with- Fig. 2-,; and meas ruling" thesupply of slurry intothe water stream. In Fig. 3 the relativepositions-of conduits stand "a; which convey the; agentsinto the watercon dint; may be reversed from thatshown.

"Figs: 4: to- 'linclusive illustrate an assemblage oi apparatusadaptedto the continuous clarification ofi largeveluinesof water, as formunicipal purposes:

A plurality offilters 4'0, not less-than three andpreterablyaconsiderably larger number, are conelected" in parallel tothe discharge of a supply pump H-by-means--ofa branched conduit 42;-the.

branchesdischarging into the lowerchamber of eachfillter.Abranchedofitake conduit weenmeets the upper chambers of the filterswith a place of disposition of" the clarified-water; e. g, a pipeline,tanker reservoir.-

3 second pump- M-has'it-s suction'side connected with olariiled watenmain- 43 and has its discharge side connected through a branchedconduit-with the upper chamber of each filter.

A- branched conduit 45 connectsthe lower chamber ofi eachfilter-with aplace oi disposition spent filter cake slurry. Each branclrof: eachconduit is: provided with a stop value, as indicated at m; I30, 450 and:W.

A-slurry-tank imis-fed-with a measured-stream.

of; filter-aid from a bin 5| by a screw feeder 52, witha solution ofaluminum sulfate or other fl'occulatin'g salt from a tank 53 through avalved pipe 54. Acontrolled; stream of water, whichmay be taken fromconduit 42, is fed continuously into-tank filkthrough valved pipe 55'.The rel-ation of the filter-aid and water feeds is such astomaintain-the contents of thetan-k in the form of a shirry; while theieedof salt solution i promentioned,- to. the earth feed in a desiredrelationl A measuring pump 56 introduces astream of the oartmsalltslurry: into water supply. conduit 51 which entersithe suction side ofpump 41 to feed the system with the turbid: water to be clarified. Iform of filter illustrated in these'figures, and which will beunderstood to be illustrative only, is'shown in more detail: in Fig. 6-.This device consists of two relatively short rings proaddedwith curvedheads and mating flanges, which may be held together by clampsor boltsnot shown. Between these flanges, and extending across; the area of thefilter, is the filtering ele ment: M; which is detailed in Fig. 7. Thisassemconsists, in desecending order, of a stiff, per iterated plate '61,a coarse mesh screenof heavy wire $2 to. g., A" #16 wire), a screen 63of finer wire to. g.; l6 meshitza) a. filter cloth filofsuit alblefabric is. g, parma twill), and a supporting layer 55 of the stiffscreen. These elements are scaled. between the flanges at their edges bysoft gaskets and are supported against distortion in me by grids 5.5 and6"!" of steel plate attached to the rings.

" Water containing earth and other suspensolds ontersxthe lower chamber68 through conduit .2,

valve 1M being open, "and passes upwardly through filteringfeleifnent60, depositing its solids inthe" o m of a cake onthelower face of thefil tering element. The filtered water leaves upper chamber throughconduit 3 valve #30 being open. This new continucsuntilthe thickness ofthe accumulated cake becomes such as to reduce the flow rate unduly,which with average water ll be a matter of many hours.

When this stage is reached, valves 420 and 430 are closed and valves mand 460;, are opened. Clarified water now enters the upper chamber fromdischarge conduit 43:, which is always under some pressure andfilledwith water discharged by the other filters cf-the battery. Thepressure thus shown; on the upper side of the filtering elementdislodges the cake, which falls to the bot: tom of the lower chamber andis flushed out as a slurry by a water jct i'ntroduced through pipe 10 Inthis cycle the cloth is not disturbed and will last a long time withoutcleaning or replacement. In tho'use of' a plurality of'filters inparallel,'all but one of the elements will be in operation at all timesand a single attendant, having only to switch valves, can care for agroupv consisting of numerous filters.

The remarkable claritying power of this come binatlon of dlatomaceousearth filter-aid and flocculating. salt, as compared with that of eitheragent alone, is shown by the results of the fol.- lowing laboratoryexperiments:

t1 A quantity oi'a municipal water containing a trifling quantityofmineral suspensoids and an appreciable quantity oi organic matter wasdosed with Wyoming 'bentonite in the proportion of-50 parts per.million. ,This bentonite is a colloidal solid and its suspension in theabove water is heavily turbid and practically stable, showing notendency to settle" out even on long standing. suspension','which offersavery diflicult fil tering problem was used in all the following tests.As a blank, a quantity of this suspension was filtered throughasmallcloth disc under a low head, and the quantityof: filtratecollected during" a fixed time-(21 minutes) was measured and calculatedto gatlo'ns per hour per square foot filtering surface.

('2) Samples of this suspension were treated with various proportions ofan agent containing 97.5% or a high flow-rate diatomaceous earthfilter-aid and 2.5% of aluminum sulfate (Ant-SO03). The water containingthe agent in suspension was-then filtered under conditions identicalwith those observed in Experiment- 1, the ilow-rate calculated and theturbidity determined photo-electrically. This turbidity figure wastranslated to parts per million of the same bentonite byreference to anexperimentally determined curve'obtained by progressively dil ning thesuspension to known bentonite proportions and reading theHolvetl-Gillett turbidity at each stageofdilution. v

(3)'San p1es of the suspension were treated withvariousfproportlonsofthe earth used in makingthe above agentbut' withoutthe addition of the salt, and the now-rates and turbidities weredetermined, as above described t4) Samples of the -sus zperision weretreated with constant quantities of an agent made from the abovemateflals'but containing-gradually de creasing proportionsofthefiocculating salt, the samples filteredun'der thesame' conditions,and theiflowqates' and turbldlties taken.

(5') A single s mple of the suspension was The results of theseexperiments are recorded in tabular form immediately below:

* Agents Added F1 R t T but owa e or 1 l y, Expt Gallons P. 5 Earth SaltTotal- Per cent Per cent Per cent i As the turbidity of a satisfactoryindustrial or domestic water should not much exceed 1.0 on theHolven-Gillett instrument (=13 P. P. M. on the bentonite scale) it willbe evident from the above figures that neither the earth alone nor thefioc alone even approaches a commercial'result when used in any feasiblequantity. When combined, however, they give high clarities' with verysmall doses: of the order of A of 1% earth with 4 of 1% of aluminumsulfate,'or of A of 1% of earth With of 1% of the salt. The relation ofabout 1 part salt to-40 parts earth is the most economical, at least forthis particular earth and water. It will be noted that the filtration ofwater rendered highly turbid with'bentonite is a difiicult problem andthat the total dosage of agent will-be materially less in the filtrationof river and other waters in which the turbidity is mainly due to solidsless colloidal than bentonite.

It is seldom if ever necessary to use more than 0.05% by weight of earthin this method, a quantity equivalent to about 4.-pounds per 1,000gallons of water clarified, nor more than of this quantity or 0.1 poundof the salt per 1,000 gallons. Good results may often be had with dosesof earth as small as 0.1 pound per 1,000 gallons, and with a quantity ofthe salt as low as 0.005 pound per 1,000 gallons of water. The mixtureof diatomaceous earth and salt used-in the latter instance are in theproportions of-100 parts diatomaceous earth and 5 parts salt.

In the filtration of steam engine condensate to fit it for reuse asboiler feed water the filtration system illustrated in Fig. 8 may beused.

Referring to thisdrawing, which is a diagram only and shows nounnecessary detail: the condensed water, which may contain up to 100parts per million of cylinder lubricating oil in astate of extremedispersion, is received in any tank 70. A pump 1|, capable of lifting atleast 70 pounds pressure, discharges a. stream' of the cloudy condensateinto a filtering shell 12 which is divided into compartments13 and 74 bya horizontal partition 15. From this partition a plurality of bootlegfilters 76 are projected down- ;wardly, being closed at their lower endsand opening upwardly into compartment 74. The bootlegs areoften made incylindrical form but ,are here illustrated as fiat leaves. As shown-inFig. 9, each leaf consists ofa grill 7! of, narrow metallic strips, the.grill being faced with 'periorated sheet metal 18 and-coveredwithlayers e: 19 of-a stiff wire mesh and ,of filter cloth. This assemblymay be flanged as at 8| to be inserted through an opening-in partition75. Perforations 82 are provided to permit liquid passing through thecloth to the interior of the grill to flow upwardly into uppercompartment 14.

In this compartment some oil may separate as a clean upper layer whichmay bewithdrawn from time to time by opening a purge'valve-83, The oncefiltered water, which often will still contain some finely dispersedoil, passes through conduit into a second filtering unit 85 of the sameconstruction as that above described. This unit has an oil purge valvein the upper compartment as-at 87.

-The twice filtered water, which should now be free from finely dividedoil but will contain oil globules in suspension, passes from unit 80through conduit 88 to a wetted septum separator by which the globulesare coalesced to form a liquid body. A convenient form for this elementis that of a cylindrical tank 89 having within it a cylinder 90 of heavywire mesh covered with Turkish towelling or so-called terry cloth. Thewater passes from the space outside the cloth cylinder through the clothand into the inner compartment, the oil adhering to the-cloth and beingforced through it to rise to the surface. The separated oil may bedrained through a valved outlet 83 while the water passes continuouslythrough a bottom outlet-94 so-arranged as to maintain the tankconstantly filled with liquid.

In the use of this apparatus the filterleaves are precoated with afilter-acid, such as finely comminuted diatomaceous earth, having theproperty of agglomerating the extremely minute suspended oil particlesinto globules large enough to separate by gravitation. For this purposea slurry tank 95 is provided with an air'jet 96 or other means foragitating the powdered filter-aid with water, and is arranged to feedinto the suction of pump H- as at 91. A desired quantity of thefilter-aid, brought to the condition of a thin slurry, is fed into thefirst filtering unit 12 in which it forms a coating on all of the filterleaves simultaneously. As only clear water passes through to the secondunit 85' a branch feed pipe 98 and diversion valves 99, I00 and llll areprovided to bypass the first unit and feed slurry directly into unit 85.

In passing through the successive units of the system, all ofthesuspended oil particles, which initially are too small to separate bygravitation in any feasible time, are coalesced into larger oilparticles or globules capable of being agglomenated into an oil body bythe wetted septum. Provided the filter-aid is sufiiciently efiective forthis purpose, the back pressure on the pump dis-'- charge builds up veryslowly and a large quantity of Water may be treated by a, single precoatbefore the maximum pressure for which the system is designed is reached.This operation differs from the filtration of domestic orindustrialWater previously described in that, after the cake becomes saturated,the liquid suspensoid tobe separated from the'water is not retained onor in the filter cake, but is passed through it to be parted from thewater in a final stage of gravity separation. Thus .--there is no needfor adding filter-aid to the Watenduring the filtering cycle, which willnot be lengthened "thereby, and the original precoat is effectiveuntilit becomeschoked by emulsion particles which the filterraid isunableito resolve; In this-operation the effectiveness of the filter-aidis measured, first by its ability completely to coalesce the suspendedoil and to deliver a water free from turbidity, second, by the length oftime which elapses before the precoat becomes choked at any giventhroughput per square foot of filtering area.

The agent above described has been found to be highly effective for thetreatment of condensed water containing suspended oil. In the followingexperiment a test filtering assembly having a total of 25 square feetsurface was fed at the rate of 1 gallons per square foot per minute witha steam engine condensate containing 70 parts per million of steamcylinder oil, the feed temperature being maintained at 125 F.

The leaves were first precoated with a diatomaceous earth filter-aid ofgood quality, the quantity applied being 2.46 ounces per square foot ofcloth surface. The feed was then started and the rise in pressureobserved hourly at gauge I02, this gauge indicating the back pressure ofthe entire system. As shown by curve I of Fig. 10, the pressure rose sorapidly that the limit pressure was approached in four hours, atwhichtime the use of this earth was discontinued.

The leaves were then cleaned and again precoated with an example of theagent of the invention, the same grade of diatomaceous earth filter-aidintermixed with 2.5% by weight of aluminum sulfate. This run wascontinued for 48 hours, at the same feed rate as in the first test, atthe end of which time the pressure on gauge I02 had risen to 29 pounds,as shown by curve 2 of Fig. 10. Curve 3 of this figure shows thepressure curve for guage I03, indicating the back pressure of the secondfiltering unit plus that of the wetted septum separator, while curve 4shows the pressure curve for gauge I04, the back pressure of theseparator alone.

In this experiment each square foot of filtering surface clarified 4320gallons of water with the use of 2.46 ounces of the mixed agent, or atthe rate of 28,000 gallons of water per pound. As the pressurethroughout this test advanced in substantially a straight line, and hadrisen only 17 pounds in 48 hours, the indications are that at leastdouble this quantity of water would have been treated before thepressure rose to 10 the 50 pounds for which this test set was designed.

Curve 5 of Fig. 10 shows the rise in pressure (for the entire system)when ferrous sulfate was used as the flocculating element of the mixedagent in place of aluminum sulfate. The rise in pressure was more rapidthan in the first experiment and the final throughput would have beenless, but the result was commercially valuable. In all of theseexperiments the clarity of the efiiuent water was such as correspondedwith an oil content not exceeding 0.2 part per million.

I claim as my invention:

1. An agent for purifying water by filtration consisting substantiallyof 100 parts of a diatomaceous earth filter-aid having an initially highflow rate and low inherent clarifying power intimately mixed with about0.5 to about 5 parts by weight of aluminum sulfate.

2. A water purifying filter aid consisting essentially of diatomaceousearth filter-aid having an initially high flow rate and low inherentclarifying power intimately mixed with a minor proportion of a metalsalt which forms a flocculent precipitate in slightly basic water, saidsalt being selected from the group consisting of the sulfates of ironand aluminum, the proportions of said salt being in the range of about0.5 to about 5 parts by weight of salt per 100 parts by weight ofdiatomaceous earth.

CHARLES A. FRANKENHOFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 20,844 Calvert et a1 Sept. 6,1938 935,695 Schultze Oct. 5, 1909 1,993,761 Tippins Mar. 12, 19352,217,466 Baylis Oct. 8, 1940 2,284,827 Lindsay et al June 2, 19422,311,713 Thomas et a1 Feb. 23, 1943 2,338,958 Muskat Jan. 11, 1944OTHER REFERENCES Non-Metallic Minerals, Ladoo, McGraw-Hill 00., N. Y.,1925, page 196.

